The native heart valves, and in particular, the aortic valve, has a complex geometry that endows both ideal opening and closing geometries through an anatomic joining of a tubular inflow structure of the left ventricular outflow tract and an expansion of the valve sinuses above the hinging point of the valve leaflets defined by the aortic valve annular ring, part of the fibrous “skeleton” of the heart.
For the purposes of discussion and definition in the ensuing descriptions, the “upper”, downstream outlet structure of the native aortic valve above its hinging point contains three valve “cusps” of a generally spherical contour with central mobile portions termed “leaflets” that are induced by fluid pressure gradients to meet centrally to close and to move radially outward to open in valve operation. The cusps are further continuous with downstream curved tissue walls meeting the tubular great vessel, the aorta, at the “sino-tubular junction”. Each cusp and its upper, downstream extension above the level of leaflet closure (“coaptation”) are a continuous structure of a generally spherical contour and together define the envelope of the “sinus of Valsalva”. Typically, surgical prosthetic valves are implanted by excision of the diseased native valve leaflets at the level of the annular ring, and suturing of the prosthetic valve at this point, thus replacing only the opening geometry of the valve and leaving the outer structures of the cusps and the sinuses of Valsalva, the anatomy that confers proper closing geometry, generally intact.
Surgical valve prostheses are generally constructed as analogs to this central portion of the native valve geometry involved in the opening phase of the valve cycle. This approach to modeling the replacement valve prosthesis is enabled by the nature of the surgical technique: the replacement valve is sutured into the valve seat under direct vision. In contrast, a percutaneous stent-mounted heart valve (“PHV”) is typically a construct in which the operating valve membrane leaflets are mounted and confined within the tubular envelope of a collapsible frame for effective transvascular delivery.
Further, in order to preclude valve regurgitation, the base of each leaflet must lie in exact apposition to the valve seat to form a seal, a condition that is difficult to satisfy without implantation under direct vision. Even then, since the diseased native valve would not be removed and its axial geometry is often distorted, it may not be possible to seat a PHV exactly under any circumstances. Thus, a cylindrical cuff layer, interior or exterior to the frame, is usually employed that acts as a seal and provides some latitude in the positioning and alignment of the PHV along the axis of flow, allowing for reliable and effective PHV implantation and minimizing the risk of significant valve regurgitation. Finally, the diseased native valve leaflets, when pushed outward by the deployed PHV frame, may themselves form a barrier separating the sinuses of Valsalva from the leaflets of the PHV, then disrupting the native closing geometry of the valve so that the sinuses are no longer continuous with the pressurized space above the PHV leaflets.
These issues illustrate some of the challenges to the formation of a PHV; that is, how to confine operating leaflets within a partially sealed tubular structure while preserving ideal opening and closing valve behavior without the benefit of the natural mechanism of the sinuses of Valsalva in a single valve and leaflet geometry, such as the separate and distinct upper and lower geometries of the native valve. As such, there is a need for additional devices, systems and/or methods that address one or more of the problems or shortcomings noted above.